From The Editors Science

NASA’s ORISIS-REx Finds Evidence of Water on Asteroid BENNU

It took NASA’s NORISIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) more than two years to reach asteroid Bennu, but just about a week to make a stunning discovery that has got mission scientists excited earlier than expected.

The spacecraft reached the proximity of Bennu on Dec 3, and by Dec 10, spectroscopic surveys of its surface revealed the presence of hydrated minerals, signifying that the space rock had interacted with the ‘elixir of life’ at some point in its past.

Although NORISIS-REx’s onboard spectrometers didn’t detect water per se, they did find hydrogen and oxygen bonds called hydroxyls trapped in clay-bearing material all over Bennu’s rock-strewn topography.

Speaking at a press conference at the American Geophysical Union (AGU) meeting in Washington DC, on Dec 10, Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center, said the discovery was “evidence of liquid water in Bennu’s past.”

“It’s one of the things we were hoping to find,” she said. “This is really big news.”

“The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the solar system, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics,” Simon said in a NASA press release.

Dante Lauretta, the OSIRIS-REx principal investigator at the University of Arizona in Tucson, said in the press release:

“Our initial data show that the team picked the right asteroid as the target of the OSIRIS-REx mission.

“We have not discovered any insurmountable issues at Bennu so far.

“The spacecraft is healthy and the science instruments are working better than required. It is time now for our adventure to begin.”

Over the coming months, the NASA spaceship, which is on an asteroid probe and sample-return mission to Bennu, will make increasingly closer passes of the asteroid, entering orbit on New Year’s Eve.

It will then begin mapping the asteroid to identify the best possible sample site before making a slow descent to the surface to collect samples using its robotic arm.

OSIRIS-REx is capable of making as many as three attempts at collecting the samples, after which it will have to begin its return journey, with its precious cargo of Bennu samples safely tucked away inside a Sample-Return Capsule (SRC).

The SRC is expected to re-enter Earth’s atmosphere and land at the US Air Force’s Utah Test and Training Range on Sep 24, 2023.

“When samples of this material are returned by the mission to Earth in 2023, scientists will receive a treasure trove of new information about the history and evolution of our solar system,” Simon said in the press release.

Analysis of samples from Bennu may offer some clues to the origins
Analysis of samples from Bennu may offer some clues to the origins

Mission scientists believe that Bennu, which is just 500 meters across, is too small to have held liquid water on its own and is, likely, a broken-away part of a larger parent asteroid that actually hosted the water at some point.

“We targeted Bennu precisely because we thought it had water-bearing minerals and — by analogy with the carbonaceous chondrite meteorites that we’ve been studying — organic material,” quoted Lauretta as saying.

“That still remains to be seen — we have not detected the organics — but it definitely looks like we’ve gone to the right place,” she added.

“We have an awesome asteroid to explore,” Lauretta also said, adding that “it’s a dream come true, and an honor and a privilege to be able to lead a program like this for NASA and for the United States and, really, for the world.”

The OSIRIS-REx sample-return undertaking is the third planetary science mission in NASA’s New Frontiers program, after the New Horizons and Juno missions, launched in 2006 and 2011, respectively.

The $800-million mission does not include the $183.5-million Atlas V rocket, which lifted off with OSIRIS REx from the Cape Canaveral Air Force Station in Florida on Sep 8, 2016, releasing the spacecraft 55 minutes later for its onward journey to where it is making exciting news now.

The five main objectives of the mission, as listed by Wikipedia, include:

  • Return and analyze a sample of pristine carbonaceous asteroid regolith in an amount sufficient to study the nature, history, and distribution of its constituent minerals and organic material.
  • Map the global properties, chemistry, and mineralogy of a primitive carbonaceous asteroid to characterize its geologic and dynamic history and provide context for the returned samples.
  • Document the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site in situ at scales down to millimeters.
  • Measure the Yarkovsky effect (a thermal force on the object) on a potentially hazardous asteroid and constrain the asteroid properties that contribute to this effect.
  • Characterize the integrated global properties of a primitive carbonaceous asteroid to allow for direct comparison with ground-based telescopic data of the entire asteroid population.

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